1. Field of the Invention
The present invention relates generally to an information recording and reproducing apparatus for successively recording and reproducing information, and more particularly, an information recording and reproducing apparatus capable of emulating a rewritable optical disc as an optical disc of the type in which recording is permitted only one time and reading is permitted many times, but no rewriting is permitted.
2. Description of the Prior Art
It is generally known that an optical disc can have information recorded thereon in a high recording density which may be about 10 or more times that recordable on a magnetic disc. The high recording density primarily owes to the high converging characteristic of a laser beam and tracks narrowed in pitch.
An optical disc called "WORM" (write-once read-many type) has a useful life longer than 10 years and is characterized in that recording is permitted only one time and reading is permitted many times, but no rewriting is permitted in principle.
The recent technical progress of optical disc media makes it possible to put to practical use media in which rewriting of data is permitted as similar to magnetic media. Magneto-optical disc media, phase change type rewritable media, and the like are in practical use as such optical disc media. Nowadays, environmental characteristics required to store the optical disc media are remarkably improved, as compared with those for magnetic tapes. Furthermore, by the use of an ordinary rewritable optical disc and a drive therefor, emulation of a "WORM" operation is performed in which recording is permitted only one time and reading is permitted many times.
In order to impart a "WORM" function to the optical disc and the drive therefor, "WORM" (information) indicating that the optical disc is a "WORM" disc is pre-recorded as bits on control tracks whereas the disc drive is made to perform a "WORM" recording operation based upon the "WORM" information recorded on the control tracks such that data recording is permitted on unrecorded sectors but prohibited on recorded sectors.
Since the rewritable optical disc and a "WORM" emulated optical disc originate from the same recording medium, it is only necessary to add to the disc drive a function required for handling the "WORM" information and that required for emulating the "WORM" operation. Accordingly, the disc drive can be considerably simplified, as compared with the case where the same disc drive is used for recording on and reproducing from the ordinary rewritable optical discs and the "WORM" optical discs which are different from each other in optical characteristics and recording principles.
In an information recording and reproducing apparatus employing the conventional "WORM" optical discs, data recording is performed on unrecorded sectors by modulating a laser beam emitted from an optical head at a strong recording power while the laser beam is being focused on a desired track. In data reproducing, a considerably weak laser beam is initially applied to the optical disc, and upon receipt of a light reflected therefrom, a reproducing signal is generated and then demodulated
In the "WORM" optical disc, since the data recording is permitted a single time, it is necessary to record data on the unrecorded sectors successively from the beginning of a track. In the data reproducing, it is important to find out the end of recorded sectors from the viewpoint of high speed handling of file management information such as the so-called directory with the reasoning that the newest data exist on sectors to which latest recording has been performed.
FIG. 1 depicts an arrangement of data in a conventional "WORM" optical disc 33. The optical disc 33 stores data 34 of recorded files and a directory 35 for controlling address information of sectors on which the data 34 have been recorded, and includes an unrecorded region 36. The data 34 and the directory 35 are successively additionally recorded on the unrecorded region 36 from the outermost and innermost portions towards a medial portion of the optical disc 33 in the direction shown by arrows X and Y, respectively.
How to record data will be discussed hereinafter taking the case where data (b) are additionally recorded on the optical disc 33.
(1) A disc drive checks the presence or absence of envelopes of recording signals from the beginning of the directory 35 in order to detect a first sector S2 having no envelope. As a result, the latest directory DIRa is found out from a sector S1 immediately ahead of the sector S2.
(2) From the directory DIRa, a last sector S3 can be known on which the end of the data 34 has been recorded. The data (b) are then recorded from a sector S4 to a sector S5.
(3) The disc drive adds address information of the recorded data (b) (from the sector S4 to the sector S5) to the information of the directory DIRa and records a new directory DIRb from the sector S2.
A "WORM" optical disc can be emulated in the above-described manner.
However, since data must be recorded on the unrecorded sectors, it is always necessary to find out the position of the unrecorded sectors at the time of disc replacement. Furthermore, when the track density is made higher to raise the recording capacity, the use of the detection of the envelopes of the recording signals makes it difficult to correctly find out the latest recorded sector. This is primarily due to a crosstalk between tracks. A crosstalk signal occasionally leaks out of a recorded sector to an adjoining unrecorded sector and an envelope thereof is subsequently undesirably detected.